It’s pretty crazy how many different diseases are floating around out there and how any of us could potentially be affected by them at any time.

If you’re paranoid, maybe you should stop reading right now…just giving you some fair warning.

What’s the rarest disease you’ve encountered?

Doctors of AskReddit shared their stories.

1. Wow.

“Rare and interesting would be Pentalogy of Cantrell which has the heart outside of the chest because the sternum has not fused.

Id seen it before with just a bit of the heart on view, but with this kid it was completely out: you could see pretty much the whole heart with the aorta and lung vessels all that was holding it, the heart just beating away.

I’d done adult cardiac for a bit but this was a little different. Tiny. We covered it with a polystyrene cup, until the kid went or theatre to have it pushed back inside.

It’s meant to be 1:65,000 live births.”

2. Pretty rare.

“Anti-NMDA receptor encephalitis. One in 1.5 million.

Psychotic symptoms (auditory or visual hallucinations, paranoia, delusions) due to an autoimmune disorder where your body produces antibodies against NMDA receptors in your brain.

We’ve seen 2 this past year at our hospital. The real incidence of this could be higher than one in 1.5m but might not be tested for often enough. Once someone gets labeled a “psych” patient, consideration of medical etiologies often goes out the window.”

3. Awful.

“The rarest I’ve encountered is KID Syndrome (Keratitis Ichthyosis Deafness).

A 5 year old, very sweet, blind girl who literally had rough, thick, opaque skin on the surface of her eyes.”

4. This is crazy.

“Pseudocyesis or hysterical pregnancy, in a woman who was an inmate in the psych wing of a prison I rotated through.

She thought she was pregnant with Jesus’s triplets and had grown a massive pregnant looking belly, was producing milk, etc.”

5. Never heard of this.

“Gorham’s disease, aka vanishing skull syndrome.

A softball size area of my patient’s skull disappeared and left behind a soft spot.

She ended up with a plastic plate to protect her brain. Crazy disease.”

6. OMG.

“We had a patient once, a young girl, who was so sick that it broke our data analysis pipeline.

When the code ingested a genome sequencing sample, it attempted to detect the chromosomal s** of the patient. It was using two metrics: the sample was considered female if it (1) lacked Y chromosome, and (2) was heterozygous on X chromosome, implying there were two copies of it. Otherwise the sample was considered male.

This one sample registered as female on metric 1 (no Y chromosome) but male on metric 2 (very little heterozygocity on X chromosome), which was not anticipated and resulted in our pipeline crashing.

Upon investigation, it turned out that the parents of that poor girl were brother and sister to each other. As a result, she had very little genetic variation throughout her genome, not just X chromosome, and was consequently very sick, with a plethora of diseases typical for consanguineous births.”

7. Tragic.

“Harlequin ichthyosis.

In med school there was a baby born with this. Basically their skin scales up an peels removing that very important barrier so kids born with this don’t live long.

She was just a couple months old and had not yet left the hospital since birth.”

8. Sounds terrible.

“Fibrodysplasia ossificans progressiva (FOP).

A disease that calcifies soft tissue and turns it into bone. When I was a medical student our group’s cadaver had this disease. During dissections we sometimes would get poked by spiky pieces of bone in random areas of her body.

Also had a spine that resembled a small turtle shell.”

9. Yikes.

“Em coup de Sabre.

It’s a rare form of scleroderma that makes your skin looks like you’ve been cut by a knife down the center of your face.

This poor lady’s mandible actually split in half.”

10. In med school.

“I saw a 4-5 year old patient with Lesch Nyhan Syndrome on my peds rotation in med school. It’s an X-linked recessive disease that a quick Google search tells me affects about 1 in every 400,000 individuals.

It’s due to a mutation in an enzyme involved with DNA recycling. The thing all med students remember about it is for whatever reason these patients have a tendency to self-mutilate. My specific patient had to have a procedure to have all his teeth removed because he would terribly bite his arms unless he was physically restrained.

I believe he had an older brother that went through the same ordeal. So sad, but definitely one of the more memorable cases from med school.”

11. Like a zombie.

“Walking corpse syndrome – cotard delusion. 17 years in mental health and I’ve seen it once.

The belief that some or all of you is d**d. The guy was so certain he was d**d he believed he was a zombie.”

12. In Brazil.

“Brazilian doc here.

I live in a really poor part of an already poor country. When I was in my pediatric internship there was this baby wiith hepatomegaly (big liver). In my region, the first thing that you have to think about in this cases is a disease called Kala-Azar (also known as black fever or visceral leishmaniosis).

It is an endemic disease which there is a parasite transmitted by a mosquito that can infect people with compromised immune system (like people living with HIV) and kids.

This parasite infects the bone marrow and simulates clinical signs of acute leukemia, like chronic fever, spontaneous bruises and bleeding. The patient develops anemia, leukopenia (low white blood cells) and low platelets.

To compensate, some organs like liver and spleen take care of the bone marrow function to create new blood cells, and thus, get bigger. This disease is really common in my region, but really rare in other parts, especially non-tropical countries like the US.

Anyway, as I was saying, this baby girl, about 1 year old was admitted to investigate a hepatomegaly. But the catch was that she kept having those episodes of hypoactivity and sleepiness, and sometimes even faintings that would then get better after she was being breastfed.

We then checked and saw that she was having lots of hypoglycemia episodes. Her lab was normal, and she had no other clinical signs that would remind of kala-azar, besides the hepatomegaly.

The patient had Hers Disease, a genetic disorder that makes you produce less Glycogen due to an enzyme defect. Never hear of it before meeting this patient, and I think I’ll never will meet other one.

Interestingly enough, in this same time, I had a patient that was admitted with leukopenia, anemia and low platelets that was also hospitalized to rule out Kala-Azar, but he actually had Fanconi Anemia, an also really rare genetic disease.

In this one, the bone marrow slowly stops producing blood cells. Besides this, the patient also has kidney, facial, bones malformation and overall physical underdevelopment.”

13. That’s brutal.

“I took care of a woman with Fibrodysplasia ossificans progressiva.

Basically your muscles slowly calcify to bone, and every injury, even small ones speed up the process.

She was pretty much wheelchair bound and needed 24 hour care.”

14. Very rare.

“I helped deliver a baby who had spots all over.

Further blood testing revealed the baby had developed leukemia while in the mother.

Didn’t know that was really possible prior to that day. Incredibly rare.”

15. Ugh!

“Eye doctor here.

Patient had bilateral acanthamoeba keratitis. Estimated that 0.0004% of contact lens wearers will be diagnosed with this condition in ONE EYE. My patient had it in both!

Acanthamoeba keratitis is a rare parasitic infection of your cornea.”

16. They all sound bad.

“Dermatologist here. Some fun ones:

Chromhidrosis, where sweat comes out in different colors. My patient’s was blue.

Argyria, a permanent discoloration from silver overdose.

Aquagenic urticaria, an allergy to contact with water.”

17. Horrible.

“Objective tinnitus- I could lean close to the patient’s ear and hear a ringing noise coming out.

Central Deafness- patient had an anoxic brain injury and was essentially deaf even though there was nothing wrong with his ears.”

18. Scurvy.

“Actual scurvy.

Poor old man didn’t know how to cook after his wife d**d and ate nothing but biscuits…”

19. A lot of weird stuff.

“Neurologist here- we see a lot of weird stuff.

Autoimmune encephalitis (“Brain on Fire”), late onset familial neuromuscular diseases, rare presentations of cancer, or paraneoplastic disorders. But one rare one sticks out for me.

We had a patient who had come in with confusion and aphasia (trouble speaking and understanding). We got more of a workup and saw small strokes all over, but in peculiar distributions, and not ones that would explain his findings. Along with it we saw micro bleeds all over superficial parts of his brain.

Turns out he has what’s called Cerebral Amyloid Angiopathy Related Inflammation. It’s an extremely rare inflammatory subtype of a stroke disorder that we still aren’t totally sure what it is. It has similar amyloid deposition you see in Alzheimer’s, deposited around vessels, which makes them weak and prone to stroke and bleeding. It causes rapidly progressive dementia.

I presented the case to our department, a large academic center, and most had never heard or seen it in their career. A couple of the stroke doctors were the only ones who knew about it and they’d never seen it. Really interesting case.”

20. A rupture.

“Patient admitted for something unrelated starts deteriorating for no discernible reason.

Has some mild generalized abdominal pain, but other than that no specific symptoms. However, he keeps worsening to the point where he’s barely hemodinamically stable.

On the abdominal contrast CT, there’s fluid everywhere. Organs pushed against the abdominal wall. Just one enormous grey puddle from the top of his pelvis to his diaphragm.

And then, at some point, there’s a scribble of white pretty much smack dab in the middle of it all (in this context, signifying active bleeding) It was shaped like the world’s smallest firework pop, and it was nowhere close any major vessel. Everyone was dumbfounded for a hot minute.

It turned out to be a spontaneous, atraumatic rupture of the cystic artery. No surgeon in the building had ever seen one. Dude underwent embolization and made it out completely unscathed.”

21. Yowza!

“Persistent genital arousal disorder.

Having multiple orgasms a day, at any time, without any stimulation; becomes quite bothersome and uncomfortable, limits your daily activities and sleep is interrupted. Over time patients can become very hopeless.

It is remarkable the dissonance between the name and the obvious joke, and the tremendous suffering these patients endure.”

22. Genetics.

“Geneticist here.

I work in a pretty big hospital and we get hard to solve cases from all over the world. Some of the cases are so unique, there is literally no name yet the genetic disorder. So those would be the rarest. But for the sake of this thread, I will discuss something that is not the rarest, but is pretty rare, and one of the most interesting:

Prader Willi or Angelman Sydrome. -these are two extremely different disorders that are both caused by the same exact genetic mutation. The only difference is if the mutation occurred on the paternal chromosome or the maternal chromosome.

If it occurred on the maternal chromosome, you get Angelman Syndrome which typically results in the child being overly happy, laughing all the time with light eyes and hair color, but also severe intellectual and physical disabilities.

If the mutation occurred on the paternal chromosome you get Prader Willi Syndrome, which results in the child having excessive hunger and can literally eat him/herself to death, but with only mild cognitive disability. These kids may go a very long time not getting diagnosed and will become quite obese.”

23. With your own eyes.

“Rarest disease that I’ve seen in my career thus far would have to be leprosy.

It’s something that one hears about in antiquity and something I read about in books but I never expected to actually encounter it in my career.”

24. Scary.

“30-year-old African-American in active labor with about five family members around her. I am the pediatrician at bedside waiting for the baby to come out so I can examine him.

He comes out and all of his poor little distal limbs are severely disfigured or missing digits. Turns out he had intrauterine amniotic banding. Pieces of the amniotic sack get wrapped around limbs and digits. This causes strangulation of the blood flow and prevents development.

Worst thing I have ever seen and one in 1 million chance of happening. But mom took him in her arms and loved him all night long as if nothing was different about him.”

25. Numb chin.

“Numb Chin Syndrome.

I was just a 3rd year med student shadowing the respiratory team at a small suburban hospital. Resp were ‘post-take’, which meant that any medical patients that came into hospital over the weekend were their responsibility until they could be referred to a more appropriate specialty. Massive list of random people to see; ward round was going to take all day…

Intern says there’s a guy who stayed in A&E overnight with ‘jaw pain’ – why does he need to be in hospital? So I get sent to go do a basic assessment in the hope that we can discharge him before it gets late. When I found him he looked fine, just sitting on the edge of a trolley.

Turns out he was in his garden the previous day when he suddenly felt a really sharp burning pain in his chin. He specifically said it was on the left side of his chin, and he initially assumed he had been stung by a bee or something. But there was absolutely no redness or swelling to be seen, and after a couple of hours the burning feeling turned to pins & needles, and now he couldn’t feel anything at all.

I hadn’t a clue what was going on, so I just went through the motions of taking a full history (he felt completely well except for this numb chin). Being a student, I got my tendon hammer out and subjected this poor guy to a whole neurological exam – everything was normal except for numbness which was entirely isolated to the left side of the chin.

My priority at the time was not looking like an idiot when I went back to present my findings to the intern, so I came up with some bulls**t about how each side of the chin is supplied by the mental nerve (an unimportant branch that runs through the jaw bone and pokes out of a hole to supply the skin just over your chin).

The stressed-out intern rolled their eyes at my esoteric anatomy lesson and told me to try come up with some diagnosis so we don’t both look hopeless in front of the boss. I literally google ‘Numb Chin Syndrome’ on my phone – I was surprised to find it was actually a thing, but the only search results are random case reports from decades ago.

The main cause seemed to be ‘idiopathic’ (i.e. “we don’t have a clue either”), but there was one or two cases where the patients happened to have leukemia. I mentioned this to the intern in a vain attempt to claw back some brownie points, but I didn’t expect them to stop and look at me.

It turns out that the guy’s only past medical history was that they had had leukemia years ago (and had been in remission for so long that they hadn’t even mentioned it to me).”

Do you know about any rare diseases that most people aren’t familiar with?

If so, please tell us all about them in the comments.

Thanks a lot!